1. Field of the Invention
This invention relates generally to spark plugs, and more particularly to insulator geometry of the spark plugs, and methods of manufacturing the same.
2. Related Art
Spark plugs for use in combustion chambers of automotive or industrial engines include a center electrode and a ground electrode providing a spark gap therebetween. During operation, a spark forms across the spark gap to ignite a combustible mixture of fuel and air. An insulator surrounds and electrically isolates the central electrode, and also provides mechanical support to the central electrode. The insulator is surrounded by a metal shell which is threaded into a cylinder head of the engine. According to one spark plug design, the insulator includes a body region and a tapering nose region which are separated by an insulator seat. A gasket is compressed between insulator seat and shell to maintain the insulator in position. The preload on the gasket should be high enough to seal under all operating conditions. However, the high preload causes tensile stress around the gasket and along the insulator seat.
The insulator of the spark plug also experiences significant bending stress around the insulator seat when used in a high-output engine. These engines generate “mega-knock”or “super-knock” causing high pressure transient shock waves which create a force transverse to the insulator nose region.